Revealing and simulating the effect of hidden damage on local and full-field deformation behaviour of cast aluminium

Abstract

Pores have been the main focus of quality assurance in castings. Latest research has shown that in aluminium castings pores can form only if there is existing entrainment damage, i.e., pores are merely the visible parts of the entrainment damage, and usually invisible damage is much more extensive. However, its effect on deformation behaviour has not been previously established or observed in-situ. This work applies 2D Digital Image Correlation (DIC) to an in-situ full-field stress-strain analysis of tensile samples with a non-conventional heterogeneous stress distribution. The observations reveal that the effect of hidden damage extends far beyond its impact on fracture behaviour and is responsible for initiating local strain concentrations during deformation. By extracting local stress-strain data, FE simulations have been performed to mimic the effect of local hidden damage on the heterogeneous stress-strain field. SEM and FIB-SEM analysis has been applied to investigate the cause for the strain concentrations. The combined results show that hidden damage in the form of oxide films is not only responsible for premature fracture, but also affects the deformation behaviour of tensile samples by introducing dispersed strain concentrations.

Integrated fatigue life predictions of aluminium castings using simulated local microstructure and defects

“…This was confirmed by fractography in optical microscopy, where the fractures in category I were found to initiate at large oxide films or surface defects, while the failures in categories II-IV originated from visible pores. This topic is further investigated in an accompanying work at this conference [20].…”

“…Castings also exhibit several other types of defects, e.g., oxide films, pre-solidified particles and inclusions. Future work in this field is aimed at understanding the role of invisible defects as oxide films on static and dynamic material behaviour, e.g., as presented in a related work in the current proceedings [20]. As for hot spots, melt quality and local flow-related aspects can also be considered local defect indicators.…”